To achieve a surgeless delivery and high efficiency a sliding-vane pump should have a constant cross-sectional area of the working chamber in the transfer area, low losses for leakages and friction, and no cavitation. The mentioned characteristics should be kept for all the operational range of the displacement alteration, pumping pressure and rotor rotational speed, and should little depend on the working fluid contamination and wear of the pump elements.
Allocation of the working chamber at the face of the rotor as, for example, in the pump US570584, provides for the desired constant cross-sectional area of the working chamber, combined well with pump displacement adjustment in U.S. Pat. No. 2,581,160, RU2123602 and U.S. Pat. No. 6,547,546.
Allocation of the working chamber in the annular groove at the face of the rotor of pumps U.S. Pat. No. 1,096,804, U.S. Pat. No. 3,348,494, US894391 and U.S. Pat. No. 2,341,710 provides for rotor radial unloading and rigid fixing of the vanes in the working chamber. The main sealings between reciprocally rotating parts in such a pump are transposed to the face surfaces of that part of the rotor where the annular groove is made and hereinafter referred to as the working part of the rotor, and to the corresponding face surfaces of the cover plate of the housing abutting to the mentioned annular groove and hereinafter referred to as the working cover plate of the housing. The mentioned sealing face surfaces of the rotor and of the housing can be made flat. Therefore, technological, thermal and other clearances between flat sealing surfaces can be easily taken up by forward oncoming movement of one sealing surface towards the other due to the pressing of the working part of the rotor to the working cover plate of the housing.
To provide the mentioned sealing it is required to overcome great pressure forces of the working fluid contained in the working chamber between the face of the rotor and the working cover plate of the housing in pumping and transfer areas tending to deform the working part of the rotor and the working cover plate of the housing and to force them out from each other.
Application of mechanical means of pressing without hydrostatical balancing in the pumps intended for generating high pressure in the pressure line is not efficient because of huge friction losses.
Patent EP0269474 describes a hydrostatic component (without specifying the ways of its installation into a pump) characterized by lower influence of axial rotor deformations on the quality of the sealings and by using the working fluid pressure for reciprocal pressing of the sealing surfaces of the rotor and housing. The rotor of hydrostatical component consists of two parts the authors call “vanes' holder” and “supporting flange”. On the back face of the vanes' holder, opposite to the face with the annular groove, in the force chambers connected to the working chamber there are mounted piston-like elements sliding in axial direction and abutting the supporting flange. Thereby, the clearances between the housing the authors call “guideway carrier” and vanes' holder are taken up by axial movement of the mentioned piston-like elements out of force chambers of the vanes' holder. Working fluid pressure forces exerted against the vanes' holder from the side of the working chamber are transmitted via mentioned force chambers and piston-like elements to the mentioned supporting flange. But the described hydrostatical component does not provide for any means of hydrostatical balancing from the opposite side of the supporting flange. The authors point out that according to the essence of the invention the mentioned fluid pressure forces are compensated by flexible deformation of the mentioned flange making the vanes' holder free from axial deformations but the rotor as a whole remains hydraulically imbalanced.
According to the essence of the described by the authors of EP0269474 invention providing for unloading of the sealing pair of friction of the vanes' holder with the guideway carrier and transference of the forces to the static contact of the piston-like element with the deformable supporting flange, the mentioned static contact seals the force chamber and the vane chamber connected to it. When the vane axially moves out of the rotor the fluid goes to the vane chamber through the channels in the vane. Increase of rotor rotational speed and axial speed of the moving forward vane results in increasing of the pressure drop in the mentioned vane channels. If the pump is operated in a self-suction mode, i.e. inlet pressure is equal to the atmospheric pressure, at the certain speed of the rotor rotation hereinafter called the maximum speed of self-suction there appears cavitation in the vane chambers. Besides the increase of noise and pulsations the cavitation leads to significant losses of useful power and efficiency of the pump. Therefore cavitation effects are considered here in one line with the losses on friction at the face seals of the rotor and of the vanes as the factors of dissipative losses decreasing the efficiency of the pump. High tendency to cavitation and therefore low value of the maximum speed of self-suction is a significant disadvantage of the said hydrostatical component.
Patent EP0265333 describes an embodiment of hydrostatical differential gear with hydrostatical rotatory thrust block mounted between the back face of the vanes' holder and supporting flange rotating at different speeds. The mentioned hydrostatical rotatory thrust block is a simple thin ring rigidly fixed to the vanes' holder at rotation and provided with chambers located opposite the supporting flange. Each of the mentioned chambers is hydraulically connected via the calibrated orifice to the opposite force chamber on the basis of hydrostatical bearing principle the authors call “oil thrust block”. Due to that pressure forces are transmitted to the supporting flange, and its deformation influences the leakages less than the similar deformation of the vanes' holder. The authors point out that deformations of the mentioned rotatory thrust block replicates deformations of the supporting flange. It means that pressure forces of the fluid acting on the rotatory thrust block from the side of the vanes' holder exceed the sum of pressure forces of the fluid from the side of the flange and elastic forces of the rotatory thrust block and cause an increase of deformation of the rotatory thrust block as long as deformation of the rotatory thrust block is sufficient for abutment to the supporting flange. In fact, principle of operation of the oil thrust block as a hydrostatical bearing assumes a dependence of the pressure in the rotatory thrust block chambers on correlation of the pressure drop on the calibrated orifice and pressure drop in the clearances between the supporting flange and rotatory thrust block. Therefore, as long as the mentioned clearances are large the pressure in the rotatory thrust block chambers is significantly lower than that in the force chambers, and due to this difference in the pressure forces the rotatory thrust block shifts closer to the supporting flange. With the decrease of the clearances the pressure in the rotatory thrust block chamber increases and becomes equal to the pressure in the force chamber which the rotatory thrust block chamber is connected to via a calibrated orifice at a complete absence of leakages from the oil thrust blocks only i.e. when the rotatory thrust block entirely abuts to the supporting flange. To achieve the mentioned abutment it is required to deform the rotatory thrust block in conformity with the flange deformation. For that it is required to provide significant hydrostatical imbalance of the rotatory thrust block.
The mentioned elastic deformation of the rotatory thrust block required for it's tight abutment to the supporting flange causes increasing of friction losses. When the flange is deformed by pressure forces of the fluid and the thrust block is abutted to the flange at first a partial reciprocal contact of the deformed flange and non-deformed thrust block appears followed by thrust block deformation. In this case elastic forces of the thrust block being overcome for its deformation cause proportionate friction losses between the rotatory thrust block and the supporting flange in the spots of partial contact. The mentioned thrust block is forced out from the flange by pressure forces of the fluid continuously distributed in insulating clearances, and it is pressed to the flange from the side of the force chambers by pressure forces distributed discretely, i.e. dropping to zero in the intervals between the force chambers. To provide good insulation when such method of pressing from the side of the force chambers is used the rotatory thrust block should be rigid enough. Therefore at significant pressures the said elastic forces of the deformed thrust block are great and the corresponding friction losses are significant.
To provide small leakages at zero or small clearances of micrometers order hydraulic resistance of the mentioned calibrated orifices should be comparable to the resistance of such microscopic clearances. It does not allow using the back face of the rotor for intake the fluid into the vane chambers via the cavities in hydrostatical thrust and the cavity in the housing. This, in its turn, does not allow to get rid of the above mentioned disadvantage of such machines, namely increased tendency to cavitation.
Besides, such use of hydrostatical bearing with calibrated orifices for decreasing friction forces results in lower reliability of the machines. Firstly, when suspended particles get into the fluid the mentioned microscopic calibrated orifices may become blocked up resulting in great increase of pressing forces of the thrust block and of the friction losses and speeding-up of wear. Secondly, in case of local defects on the sealing surfaces the leakages from the mentioned chambers of the rotatory thrust block increase and the pressure in the rotatory thrust block chambers drops. Tighter pressing due to the increasing difference of the pressures in this case does not reduce the leakages and result in balancing but rather causes greater losses on friction and quicker wear of the sealing surfaces. Volumetric efficiency can change insignificantly due to such an additional leakage from the chamber of the oil thrust block while the losses on friction can increase significantly.
For hydraulic balancing of the rotor of hydrostatical differential gear described in patents EP0269474 and EP0265333 the authors provide for a possibility to use a pair of hydrostatic components of the mentioned type in two embodiments.
The first embodiment has two guideway carriers mounted at the both sides of one central vanes' holder. The mentioned force chambers are made in the back part of the guideway carrier performing the function of the sliding seal fastened to the housing. In this case there is formed one whole rotor with two working chambers in two annular grooves on the opposite faces of the rotor similar to that described in details in the patent U.S. Pat. No. 3,348,494.
The second embodiment has two vanes' holders mounted at the both sides of one central guideway carrier. Vanes' holder via the force chambers bears against the supporting flanges that rigidly joint each other by means of a hollow cylindrical body forming a uniform rigid element the authors of patent EP0265333 call a “sealed crankcase”.
In both embodiments of double machine the unit formed by two guideway carriers hereinafter shall be called stator unit or housing as the location of suction and pumping ports relative to it is not changed during the rotor rotation. The first of the described embodiments of double symmetrical machine hereinafter shall be called a machine with internal rotor or with force closure to the housing, while the second embodiment shall be called a machine with internal stator or with force closure to the rotor.
In both mentioned embodiments pressure forces of the working fluid exerted between the rotor and housing in pumping area in one working chamber are balanced in the second working chamber by reflection symmetric forces provided that both working chambers are made reflection symmetric relative to the plane perpendicular to the axis of rotor rotation.
In transfer areas axial balancing of the fluid pressure forces acting upon the rotor does not depend on working chambers symmetry only and requires special consideration.
In forward transfer zone at rotor rotation there arise and move closed transferred volumes separated from suction and pumping areas by sliding insulating contact of vanes with a forward transfer limiter, of vanes with vane chambers, of insulating surfaces of the rotor with the corresponding surfaces of the housing and by other clearances between the rotor, the vanes and the housing. Local pressure in each of the transferred volumes at other things being defined depends on the difference of the leakages entering this transferred volume and leaving it, depending in their turn on the character of abutment of the surfaces of all sliding contacts insulating the mentioned transferred volume for different rotation angles during its rotation. The character of abutment of the surfaces of the sliding insulating contact here and hereinafter means forms and hydraulic resistance of the clearances between such surfaces as functions of two parameters: rotation angle of the rotor and angular coordinate of the contact point relative to the chosen point of the housing. Individual character of abutment of each pair of surfaces in each machine is caused by technological inaccuracy during manufacturing and local defects appearing on the mentioned surfaces as a result of wear and resulting in spread of insulating clearances resistance in different areas of the housing and for different rotation angles of the rotor. The spread of resistance of clearances can lead to significant spread of local pressures arising in different transferred volumes. Similar statements are also true for backward transfer area.
The double symmetric machine described above with internal stator has no means of local pressures balancing in transfer areas, and transferred volumes in transfer areas of both symmetric working chambers are not connected to each other. Double symmetric machine with internal rotor U.S. Pat. No. 3,348,494 has channels in the rotor connecting symmetric vane chambers. But symmetric cavities formed in both annular grooves in transfer areas between the vanes are not connected to each other. Therefore, due to individual character of abutment of the surfaces of insulating contacts each working chamber has different local pressures in transfer areas and rotor balancing is not achieved. The mentioned variable difference of the pressure forces acting upon the rotor in two symmetric chambers results in proportional losses on friction in face seals. Arising local defects on sealing surfaces of the vanes, rotor or housing as a result of wear, for example, leads to greater spread of hydraulic resistance influencing local pressures in the transferred volumes. Even in case of minor change in total leakages insignificant for volumetric efficiency it results in greater amplitude of the mentioned variable difference of pressure forces, greater friction from the side of the smaller local pressure, i.e. from the side of larger wear, and speeding up of the further wear.
In the pump under patent U.S. Pat. No. 3,348,494 axial movement of the vanes in the rotor is provided by a special vanes drive mechanism rather than by springs. It consists of a cam slot mounted on the housing along which the side lobes of the vanes going through special driving windows in the rotor slide. One skilled in the art can find that such vanes drive mechanism should be hydraulically insulated from the working chambers.
Such embodiment of the vanes drive mechanism outside the working chamber reduces the losses on vanes friction against the surfaces of the housing but increases dependence of local pressures on the character of abutment of the surfaces of sliding insulating contact of the vanes with the walls of vane chambers providing hydraulic insulation of the vanes drive mechanism. Change of the mentioned character of abutment due to wear results in the increase of leakages between the cavities of the working chamber and the cavity where the mentioned drive mechanism is installed that leads to the spread of local pressures.
In both embodiments of double symmetric machines the vane moving out of the vane chamber in axial direction is substituted by the fluid coming through the channels in the vane itself. Therefore cavitation losses remain a significant disadvantage of such design.
Embodiment of the pump providing for hydraulic means of rotor balancing and being not a subject to cavitation in vane chambers is described in patent RU2215903. It describes reversible rotor machine containing two annular grooves forming working chambers at both faces of the rotor. Through openings for the vanes pierce both annular grooves. Each cover plate of the housing has axially movable forward transfer limiter the authors call “adjusting element” and backward transfer limiter the authors call “partition”. The feature of the reversible machine is mutual antisymmetry of the two mentioned working chambers, and namely, that there is an adjusting element of the second working chamber mounted opposite the partition of the first working chamber, and a partition of the second working chamber mounted opposite the adjusting element of the first working chamber. “Working cavities” here understood by the authors as suction and pumping cavities of both chambers located in axial direction opposite each other are connected to each other by channels. Thus, the suction cavity of the first working chamber is connected to the pumping cavity of the second working chamber located opposite to it, and the pumping cavity of the first working chamber is correspondingly connected to the suction cavity of the second working chamber.
When the vane is moving out of the rotor into the suction cavity of the working chamber the fluid from the opposite pumping cavity of the other working chamber fills up the vacated volume in the vane chamber through the vane chamber of big cross-sectional area. So tendency for cavitation in the vane chambers is not characteristic for such a design.
When such machine is in operation there is high pressure set in one of the connected pairs of working cavities and low pressure in the second pair correspondingly. A possibility of hydrostatical rotor balancing in the zones of suction and pumping cavities location in such machine is evident.
In transfer areas due to antisymmetry of the working chambers there are different means of insulation and different configuration of the transferred volumes for opposite rotor faces. Between the rotor and the adjusting element there are formed confined in the annular groove transferred volumes insulated by the faces of the vanes sliding along the adjusting element. Between the rotor and partition located opposite the mentioned adjusting element there are formed confined in the vane chambers transferred volumes insulated by the sections of the bottom of the annular groove sliding along the mentioned partition. Distribution of the transferred volumes pressures and pressures in the clearances of the mentioned sliding insulating contacts depend on form and size of the mentioned clearances, i.e. on character of abutment of surfaces of the mentioned sliding insulating contacts of the sections of the annular groove bottom with a partition and of vanes with an adjusting element. Non-identity of pressure distribution at the opposite faces of the rotor generates variable differential forces acting upon the rotor in each transfer area even if the mentioned contacting surface is ideally flat.
Appearance, for example, as a result of wear, of local deflections from flat form, scratches and other local defects on the sealing surfaces of the adjusting elements, partitions, bottom of the annular groove, and vanes faces changes the character of abutment of the surfaces of the mentioned sliding insulating contacts thus changing the mentioned distribution of pressures and correlations of local pressures. That in its turn even in case of insignificant change of total leakages leads to significant increase of the amplitude of the mentioned variable differential pressures, increase of friction and quicker wear.
Provision of face sealing between the rotor and cover plates of the housing for both faces of the rotor by means of precise manufacturing only as in U.S. Pat. No. 3,348,494, for example, is not reasonable, as change of clearances resulting from thermal expansion, deformations and wear as a rule exceed permissible clearances in the seals operated at high pressures. So the structure of a rotor machine shall also include sealing elements movable in axial direction, for example, such as a guideway carrier with force chambers at the side opposite the guideway described in EP0269474. Their imbalance also leads to the corresponding losses on friction. Such movable sealing is described in more details below.
The means reducing the influence of the character of abutment of the surfaces of sliding insulating contacts in the working chamber on rotor balancing, a solution for overcoming the described tendency of such pumps to cavitation in vane chambers, and movable in axial direction sealing elements described in RU 2175731 taken by us for the closest analogue.
The mentioned patent describes a pump with a housing including working and supporting cover plates called “housing cover plates” in the patent. The face of the rotor located opposite the working cover plate of the housing has a cylindrical annular groove going through vane chambers called in the patent “openings in the rotor” with the vanes called in the patent “displacers”. The surfaces of the rotor's face that has a cylindrical annular groove located at the both sides from this groove contact with a possibility of sliding along the faces of the sealing elements located opposite them and mounted in the slots on the working cover plate of the housing. The pump includes a backward transfer limiter, the patent calls a “partition” separating suction cavity from pumping cavity. Suction cavity is connected to inlet port the patent calls “inlet opening”, while the pumping cavity is connected to outlet port the patent calls “outlet opening”. The surfaces of the backward transfer limiter are in sliding contact with the rotor means of backward transfer insulation the patent calls “internal surfaces of cylindrical annular groove”. Backward transfer limiter is fastened to the working cover plate of the housing and can form a single integral unit with it, but it is provided that in some embodiments of the pump backward transfer limiter can be mounted with a possibility to move in axial direction and interact with the means of its pressing to the rotor. The pump contains a vanes drive mechanism the patent calls “a mechanism setting axial arrangement of the displacers relative each other”. Forward transfer limiter is formed by part of the internal surface of the working cover plate. For an adjustable embodiment of the machine the patent calls forward transfer limiter “movable in axial direction insulating element”. The second face of the rotor contacts the supporting cover plate of the housing. The supporting cover plate of the housing of the pump provides for a possibility to mount a supporting-distributing member called in the invention “supporting-distributing disc”. Supporting-distributing member can be mounted with a possibility to move along rotor's axis.
The mentioned supporting-distributing member contains supporting cavities also performing distributing functions and called in the patent “supporting-distributing cavities”. Supporting-distributing cavities are located opposite suction and pumping cavities of the working chamber and the means of their insulation (insulating partitions)—opposite transfer areas providing insulation of these supporting cavities by means of the sliding contact with the adjacent back face surface of the rotor. Each supporting-distributing cavity is connected via channels made either in the housing or in the rotor including the vanes to the opposite suction or pumping area correspondingly. The dimensions and forms of the supporting-distributing cavities are similar to those of pumping and suction cavities in the working chamber correspondingly. Vane chambers in the rotor are made as through channels connecting in suction and pumping areas to the mentioned supporting-distributing cavities.
The mentioned through channels in the vanes or in the rotor simultaneously connected to the suction cavity of the working chamber in this case are parallel-connected to each other and to the channel in the housing via the mentioned supporting-distributing cavity. It provides for significant decrease of the pump's tendency to cavitation and for significant increase of the maximal self-suction speed.
Introduction of supporting-distributing member also contributes to a certain hydraulic balancing of the rotor. A possibility of balancing in pumping and suction areas is evident.
In transfer areas the similarity of distribution of pressures at the both faces of the rotor caused by the presence of the mentioned through channels in the rotor or in the vanes makes it possible to reduce the influence of the spread of insulating clearances in the working chamber and connected local pressures on the difference of counter pressure forces acting upon both faces of the rotor. But complete balancing of the rotor is not achieved due to different configuration of the rotor faces. Incomplete balancing of the rotor results in variable difference of pressure forces acting upon opposite faces of the rotor and causing proportional losses on friction in face seals.
Pressure distribution on the back side of the rotor in transfer areas is determined by the character of abutment of the surfaces of sliding insulating contact between the insulating dams of the supporting-distributing member and the rotor. Therefore, change of the mentioned character of abutment due to appearance of any deflections from the flat form or scratches on the sealing surfaces resulting, for example, from wear leads to significant disturbance of the mentioned similarity of pressure distribution. This in its turn even in case of insignificant change of total leakages leads to significant increase of the amplitude of the mentioned variable difference of pressure forces, greater friction and quicker wear.
Let us consider other components of loss on friction in face seals.
The internal surface of the supporting cover plate of the housing has a slot with at least one sealing element mounted in it with a possibility to move along the axis of the rotor rotation. The authors point out that supporting-distributing member the patent calls supporting-distributing disc can be used as such an element. Two sealing elements are mounted in the slots on the internal surface of the working cover plate of the housing with a possibility to move along the axis of the rotor rotation.
The mentioned sealing elements are made as hollow cylinders located in the annular slots on the internal surfaces of cover plates of the housing with a possibility to move along the axis of the rotor rotation. To provide the required pressing of the movable sealing elements to the surface of the rotor the mentioned elements are supported by special force chambers made inside the housing where an increased pressure is formed. In the described machine the role of such force chambers is performed by the mentioned annular slots. To create increased pressure in the mentioned annular force chambers the mentioned hollow cylinders have through channels connecting the annular force chamber to the area of leakages in the clearance of face sealing. The value of the increased pressure in the annular force chamber is determined by the form, dimensions and location of the mentioned channels.
The mentioned movable sealing element mounted on the housing in one cylindrical slot with the same pressure in the whole volume is subject to significant over pressing to the rotor in suction area and partially in transfer areas that causes excessive looses on friction.
The patent EP0269474 points out a possibility to make several force chambers insulated from each other in the housing. Different pressures are created in these chambers, therefore movable sealing element represented by a guideway carrier supported by these chambers can be well balanced hydrostatically in the pumping and suction areas. And because of two reasons in the forward and backward transfer zones the movable sealing element is acted upon from the side of the rotor by variable forces. Firstly, the area of the transfer zones at the edges of transfer zones connected to pumping or suction areas cyclically change. Secondly, the pressure in the transferred volumes of the working fluid in the process of their forward or backward transfer between the suction and pumping zones continuously changes and their position relative to the housing also continuously changes. As a result in the transfer zones there is formed complex, continuously changing pressure distribution acting from the side of the rotor upon the movable sealing element. To create symmetrical, continuously changing pressure distribution between movable sealing element and the housing it would be required to place infinite quantity of insulated from each other infinitely small force chambers each of them connected to the corresponding point in transfer zone and isolated from the adjacent force chamber. As practically realizable number of force chambers in the housing in transfer zone is limited to rather small numbers complete compensation of the variable forces acting upon movable sealing is not achieved. It leads to variable force of pressing of the surfaces of sliding insulating contacts of the rotor to the mentioned sealing elements of the housing.
Change of the character of abutment of surfaces of sliding insulating contact of the movable sealing element to the rotor because of occurrence of local defects of the sealing surfaces, for example, due to wear, leads to greater spread of hydraulic resistances determining local pressures in transferred volumes. This, in its turn, even in case of small change of total leakages leads to greater amplitude of the mentioned pressing force, increased friction and speeding up further wear.
The amplitude of this variable component achieving significant values determines the level of losses on friction inherent in the described above pumps with movable sealing fastened to the housing.
So all the solutions for hydrostatical balancing of the rotor and movable sealing considered above do not provide for complete balancing of the rotor and movable sealing. If the character of abutment of surfaces of sliding insulating contacts is not ideal, for example, when there appear local defects of sealing surfaces due to wear, there arise great forces of pressing in friction pairs between sealing elements of the rotor and housing. A need to provide for such great pressing forces determines relatively large width of the sliding insulating contact of the sealing shoulders of face seals and in its turn further increases the influence of local defects of sealing surfaces on disbalance of the pressure forces.
All the structures described above are characterized by increased dissipative losses decreasing their efficiency. The described means of decreasing friction by means of hydraulic balancing of the rotor and movable sealing do not lead to complete balance and are not resistant to the change of character of abutment of sealing surfaces of sliding insulating contacts due to appearance of local defects and contamination of the working fluid. Even the changes of leakages insignificant from the point of view of the influence on volumetric efficiency can cause significant decrease of mechanical and total efficiency.